Sheet metal shops process sheet metal by bending and piercing the sheet metal with press brakes, punch presses, and other similar sheet metal forming machines. Typically, press brakes are hydraulic devices that utilize metal dies and metal punching tools which are shaped in such a way that when the press brake compresses the die and punch with the sheet metal in between, a particular bend or curve is formed in the sheet metal. Punch press machines, on the other hand, punch holes of various sizes and shapes in the sheet metal. To accomplish this, turret assemblies containing punching tools are positioned above the sheet metal with dies positioned below the sheet metal. With tremendous pressure, the punch press forces the punching tool downward through the sheet metal and into the die. In addition, sophisticated punch press machines have the capability to slide and rotate the sheet metal at very high speed while operating dozens of turret assemblies simultaneously.
Because both sheet metal forming methods involve metal-on-metal contact and because there is relative movement between the sheet metal and the machine surfaces and tools, it is not uncommon for the machines to scratch, gouge, or otherwise mar the surface of the sheet metal. Precoated, plated and painted sheet metal is especially susceptible to damage. With punch press machines, the punching tools and dies wear quickly, causing an increase in the clearance between the two, further resulting in rough and distorted edges around the sheet metal holes. If the application calls for highly precise holes and visually perfect bends, scratches, gouges, and rough edges are simply unacceptable. Sometimes the sheet metal machine shop is forced to deburr or smooth rough edges which adds a costly and time consuming step to the sheet metal forming process.
In recognition of this problem, some sheet metal machine shops have begun placing protective material such as paper, cloth, and plastic between the sheet metal and the sheet metal machines. Some shops coat the sheet metal with polyvinylchloride (PVC) or polyurethane film. Others coat the machine surfaces and machine tools. These materials alone have not completely eliminated the problem, and in some cases, it has actually caused additional problems.
Transference of the protective material texture is just one of the problems. Most materials have some grain or pattern associated with the surface of the material. This is especially true with woven and fibrous materials. As mentioned, press brake and press punch machines exert extremely high levels of pressure on the sheet metal. This pressure can actually transfer the grain or pattern of the protective material to the sheet metal surface. Furthermore, press brake and press punch machines are capable of moving the sheet metal around at very high speed and the use of plastic, cloth, or paper products can impede this movement. Film coatings alone, on the other hand, generally provide little protection for either the sheet metal or the tools. This is especially true when the sheet metal is harder than the tools. Typically, the tools will wear quickly and, as mentioned above, cause rough, distorted, and imprecise edges or bends. Finally, with regard to punch press machines, there are so many punching operation per minute that it is very inconvenient and time consuming to continually place and replace pieces of protective material over the appropriated sections of sheet metal.